A hemispherical reamer for reshaping at least partial spherical cavity is widely used in current medical procedures, such as, bone sockets in total hip arthroplasty (THA). A plurality of reamers invented in the past has mostly derived from an idea of “convex-concave match or spherical radius matches” design. The reamers usually comprised of a full hemispheric thin wall shell with a specific radius, a plurality of cutting surfaces projected from and helically distributed on the convex surface of the spherical shell, basically forming a hemispheric “cheese grater”. In particular, such the cutting surfaces spirally distributed around the rotational axis of the sphere and created an imaginary cutting profile along the arch of the shell cross section, which has a virtual cutting axis. The cutting axis is vertically (90-degree angle) toward the longitudinal axis of the sphere to be cut. Adjacent each cutting surface, there is opening to form a narrow passage extending from the exterior hemispherical surface into the internal chamber of the cutting shell. In the past decades, only a few alternative designs of such reamer have been developed. The prior art reamers as mentioned have common characteristics as follow:
A limited functioning life of the cutting edge: The projected cutting surfaces are made from flat panel of metal, which were stamped, punched and perforated in order to create cutting surfaces having the desired height, shape, adjacent openings, and a spherical shell. They formed “open mouth” cutting surfaces facing the surface to be cut, positioned at 90-degree angle to the latitude lines of the spherical reamer surface. Actually, under a more detailed study, such processing steps can only form a right angle cliff edge on the cutting surface and it can hardly be sharpened in any manners. This kind of processing steps and design for a cutting surface is quite different from the ideal cutting ware and easily becomes dull at the corner of the cliff edge, if the material used is not hard or thin enough or the punching tool gets dull. In order to increase the sharpness and functioning life of such cutting surface, thinner and harder materials must be used for better outcomes. However, this would increase the cost of the reamer and forming tools.
A limited total edge of cutting exposed to the surface to be cut: In either V or arched-shape of cutting surface in the prior art, only a limited tip section can intimately contact the cutting surface and is to efficiently cut the surface. Other elevated parts of the cutting surface are just support members, not being used for cutting.
Such concerns and some obvious defects of the prior art reamers have been addressed. In U.S. Pat. No. 9,101,368, (Sidebotham et al.), the concept of the functioning life of the reamer was addressed and tested. A useful result reported has shown that average functioning life of the regular cheese grater only lasted 2-6 times of uses on maintaining average bone reaming quality before it begins suboptimal operation. Such variations depend upon the design and manufacturing method of the reamer from the suppliers. There are evidences that the cliff edge of the cutting surface discussed above becomes a round shape very soon after few runs. Unfortunately, Sidebotham et al. was unable to bring a direct solution about improving the dulling problem of the cutting surface. Instead, Sidebotham et al. has adjusted the orientation of some cutting surface in to more efficiently direction of cutting for properly conducting the axial pushing force applied by the surgeon, particularly when the cutting surface is corresponding to cutting the “equatorial zone”. In order to avoid the dulling problem of the prior art reamers, one might further reduce either the thickness of the materials used for the reamer or the usage frequency of the reamer. So the concept of a disposable reamer becomes one possible path in public focus.
In U.S. Pat. No. 8,407,880, (Stamp, et al.), U.S. Pat. No. 8,435,243, (White et al.) and U.S. Pat. No. 8,679,124, (Lechot et al.), there are similar concerns as mentioned by Sidebotham et al. above. For example, the importance of precise dimensions and the labor-intensive making of a conventional reamer, instead of solving the dulling problem of the reamer. Their solutions were creating a plurality of the cutting surfaces is created by pressing or punching through a ribbon-like shim of metal, typically having a 0.2-0.5 mm thickness. Since the metal shim is relatively thin (compared to the 1-1.5 mm thickness of a prior-art acetabular reamer cup), the plurality of cutting surfaces may well be “sharp enough” at its edge for a single use purpose already, once formed and also bent for assembling. Such shim has over-molded with a spherical plastic substrate using the plastic molding process or coupled with other spherical frame or the center connector made by other materials to create a disposable reamer. Such cutting surface made by thin shim and combination with plastic substrate still did not solve the problem of sharpness of the cutting surface. In other aspect, thinner metal sheet can be used as in making regular reamer does not mean it can be a solution for a disposable one regarding to its strength and sharpness of the cutting surface. In addition, making each individual spherical radius of the reamer must be equipped with a series of corresponding tooling(s) for each part. The total tooling cost would add on to the final cost of reamer per use. If there is no large enough quantity required, the cost per use of the disposable reamer might not be less than one of reusable reamer.
The subject matter of a prior U.S. Pat. No. 8,771,275 (Xie et al.) of the present inventors is hereby incorporated into the present application. In U.S. Pat. No. 8,771,275, a new principle of reaming a hemispherical surface referring to the idea of “a ball in the cup” had been proposed. Specifically, a circular cutting element is offset by a specific distance between a center or a cutting plane of cutting element and the spherical center of the sphere and by a specific angle between a cutting axis of the cutting element and a longitudinal axis. When it rotates around a longitudinal axis, it generates a partial spherical surface. Simultaneously, the circular cutting element is able to self-turn around its own cutting axis freely. According the geometric rules, the device with such design can create a perfect hemisphere through one axial reaming. But it also exposes several disadvantages or has potential room of improvements:                A self-turning of the circular cutting element in the structure would require a complicate mechanical support of the reamer, which would limit numbers types of reamer design.        The cutting edge of the circular cutting element used has contacted the surface in pin-point manner and can only scratch the surface instead a peeling off like one in cheese grater. So the cutting efficiency of reaming is deducted and is lower than one of the cheese grater.        To be a tradeoff, the complicate mechanical structure of the reamer required would cause that some functions of the reamer is undoable or less reliable as well as too expansive.        
According to such a new cutting principle of the present invention, the circular cutting element provides more freedom on designing a better circular cutting element, in term of improving the cutting performance of the reamer. For example, better sharpness, an ideal way to cut the surface, and reducing its processing steps and final cost are desirable.